The studies proposed are directed to approach experimentally most of the present day problems in photobiology known to be of importance to man. Particularly, they are directed at the investigation and prevention of interactions of sunlight with otherwise useful chemicals with resultant sometimes unexpected, and sometimes drastic ecologic and biologically harmful effects. Approaches to be used utilize techniques of optical physics, particularly design of novel light sources and light measurement devices, photochemical studies of polycyclic aromatic hydrocarbons, various phototoxic compounds and effects of antioxidants with emphasis of the effect of photoproducts on augmentation of photocarcinogenesis, studies of the effects of ultraviolet radiation and visible light on human epidermal cells in vitro (including effects on DNA, RNA and protein synthesis, urocanic acid metabolism and DNA repair), investigations of models for measurement of UV effects (photophysiology) and experiments in clinical photobiology including restudying skin erythemia action spectra, phototherapy of icteric neonates and use of phototoxic agents in cutaneous phototherapy. A core program supporting these studies is also prepared.